Which of the following sources of employee recruitment is likely to be the most expensive?

A) advertising
B) employment agency
C) headhunter
D) employee referral

Headhunters, also known as executive search firms, are typically the most expensive recruitment source because they provide a specialized service of finding and recruiting top-level candidates, often for senior, executive, or highly specialized positions. This service includes extensive research, outreach, and vetting of candidates, which contributes to its higher cost compared to more general recruitment methods like advertising, employment agencies, or employee referral programs.